Welding electrode with contoured face

ABSTRACT

Welding electrodes with a welding face for contact with a metal surface for electrical resistance welding are provided with concentric contoured rings formed into the face. The rings may, for example, be ridges upstanding in the face or grooves depressed into the face. The contoured rings may be radially spaced with relatively flat (depending on the curvature of the face) intervening rings. When the electrode is pressed into contact with the surface of the workpiece for delivery of a welding current, the features of the concentric rings penetrate surface oxides or other conductivity barriers. When ongoing welding operations have eroded the contoured rings they may be rapidly reformed in the weld face in a surface re-dressing operation.

TECHNICAL FIELD

This invention pertains to welding electrodes for electrical resistancewelding. More specifically this invention pertains to the formation ofconcentric geometric features on the welding face of the electrode forimproved electrical contact with the workpiece.

BACKGROUND OF THE INVENTION

Current automotive vehicle manufacturing operations include, forexample, the joining of two sheet metal layers by spot welding. Vehiclebody panels such as doors, hoods, deck lids and liftgates are oftenassembled by joining inner and outer panels stamped from sheet metal ofsuitable metal alloys. Ferrous or aluminum alloys are often used. Thethickness of each sheet metal layer may vary from less than onemillimeter to more than four millimeters. Electrical resistance spotwelding is often used to join such inner and outer panels or other metalparts.

In the case of sheet metal body components, flats or flanges of two orthree components are placed together and then a series of spot weldspenetrating from the top sheet layer through into the bottom layer aremade to securely attach the panels. Welding practices have beendeveloped for such spot welding operations. Good welding practices areparticularly critical in joining aluminum sheet alloys because of thehigh electrical and thermal conductivity of the material and theomnipresent oxide coating on the surface. Similar welding challengesarise in the welding of other light metal workpieces such as parts madeof magnesium alloys. The spot welding operation is accomplished byassembling the parts in a suitable fixture and pressing weldingelectrodes against opposite sides of the overlying or touching parts atthe intended weld location. The welding electrodes usually provide bothclamping force and current commutation for the weld.

Copper or copper alloy welding electrodes are often used in weldingaluminum alloy workpieces. U.S. Pat. No. 6,861,609, titled WeldingElectrode for Aluminum Sheets and assigned to the assignee of thisinvention, illustrates some such welding electrodes.

As illustrated in the '609 patent, the electrodes are often roundcylinders with a welding face at one end shaped to engage theworkpieces. The welding electrodes are part of a welding apparatusincluding a welding head or gun that can be moved and actuated to presstwo aligned and opposing electrodes against the assembled workpieces.The apparatus then delivers a momentary welding current to theelectrodes to affect the weld. Workpiece metal layers between theelectrodes are momentarily melted by electrical resistance heating toform a weld nugget joining the layers. The clamping force, the value ofthe welding current (often single phase alternating current, 60 Hz, orrectified direct current) and current duration (several cycles of the 60cycle current) are also specified for the electrodes to be used and thewelding task.

In vehicle manufacturing or other industrial process, each welding gunis typically used to make a rapid succession of welds, for example,around the periphery of two or more overlying panels. The highelectrical and thermal conductivity in combination with the insulatingnature of the naturally-formed surface oxide of aluminum alloys (ormagnesium alloys) makes them difficult to weld using spot weldingpractices previously developed for steel alloys. In the case of lightmetal alloys, the spot welding process is sensitive to a large number ofvariables beyond the normal welding parameters of electrodeconfiguration, electrode force, weld time, and weld current. These othervariables include sheet surface oxidation, sheet surface cleanliness,sheet surface topography as well as process variations such as alignmentof the electrodes to the sheet, location of electrodes relative to thesheet edge and part radius, metal fit up, gun stiffness, alignment ofelectrodes on the gun, electrode surface roughness, and wear of theelectrode surface.

The welding faces of some electrodes are roughened by blasting withsmall steel or sand particles or abrasion with a course abrasive paperas illustrated in the '609 patent. The roughened surface ischaracterized by randomly distributed craters with peak to valleydimensions, for example, in the range of 5 to 30 micrometers and withsubstantially the same range of peak to peak spacing. This texturepermits the electrode face to penetrate an oxide film on the workpiecesurface to reduce electrode resistance (and overheating) at the contactsurface of the electrode and part. But, whether textured or not, thetips or welding faces of the electrodes may be altered by erosion or byadhesion and buildup of workpiece material after several welds. Weldingoperations must then temporarily cease while the electrode faces arecleaned, or re-shaped, or re-dressed. The redressing of grit blastedelectrode faces, for example, can require many tens of seconds ofoff-line processing.

There is a need to provide a resistance welding electrode with acontoured welding face that both improves electrical contact with aworkpiece surface and the reliability of resistance welding, anddecreases the time required for re-dressing of the welding face duringwelding operations. Such an electrode would be useful in many weldingapplications and would be particularly useful in welding light metalalloy workpieces with their oxide surface films.

SUMMARY OF THE INVENTION

This invention is applicable to electrodes or electrode caps or weldingface surfaces especially for electrical resistance welding. Suchelectrode members often have round cylindrical bodies for easy securingin the electrode holder of a welding gun. An end of the electrode may betapered from the diameter of the body to form a welding face. Thewelding face of the electrode may be machined so that the weldingsurface comprises concentric circular geometric features (ridges orgrooves) instead of the random roughened surface achieved by gritblasting. Suitably, a pattern of concentric circular ridges or groovesstarts at the center of the welding face and extends radially outwardlyover the face of the electrode. The circular contours may extend fromthe welding face onto a tapered portion of the electrode because atapered portion of the electrode may be brought into engagement with apart to be welded.

The concentric ridges or grooves are formed, respectively, to havecircular surfaces projecting outwardly from the face of the electrode orinwardly into the face of the electrode so that these formed surfacesengage and possibly penetrate the surface layer or film of a workpiece.Each (or some) of the concentric ridges or grooves may be separated fromtheir radially-spaced neighbors by a flat ring-shaped surface in theface of the electrode. By way of example, the circular ridges or groovesare suitably formed to have a peak-to-base height in the range of about20 μm to 200 μm with a peak-to-peak or base-to-base spacing (dependingon the profile of the ridges or grooves) of 80 μm to 1500 μm. Thiscircularly contoured welding face pattern is easily formed on newelectrodes.

Thus, a single-step process is provided that simultaneously provides thebenefits of both electrode dressing, i.e., electrode reshaping, goodalignment, electrode surface cleanliness, etc., with the benefits of atexturing process, i.e., improved mechanical stability, low contactresistance, and reduced external expulsion. This may be achieved bypreparing (for example, machining) electrode dressing blades to cut orotherwise produce a circular contoured surface on the welding face (atleast) of the electrode tip. This circular pattern is achieved byputting a series of fine grooves or ridges into the face of a dressingblade. For example, the circular grooves may have cross-sections thatare semi-circular or saw-tooth (triangular) or sinusoidal inconfiguration. During electrode dressing, these grooves/ridges cut andproduce corresponding ridges or grooves on the dressed surfaces of theelectrode. As an example, grooves or channels can be machined into atool steel blade using EDM machining.

The concentric circular ridge or groove design for the electrode capprovides improved welding performance of the electrode. It is also atextured pattern that can be restored very rapidly to the electrode faceas it is re-dressed for continued welding operations.

Other objects and advantages of the electrodes will become apparent froma detailed description of some exemplary preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of aligned and opposing weldingelectrodes engaging assembled sheet metal panels for a resistancewelding operation.

FIG. 2 is a schematic representation of the electrodes of FIG. 1positioned to have their welding faces re-dressed by a cutter bladeshaped for cutting concentric round ridges in the faces of the tools.

FIG. 3 is an enlarged view of a cutter blade positioned under a weldingelectrode for the formation of concentric round ridges in the face ofthe tool.

FIG. 4 is an enlarged view of an electrode with a tapered conical tipand a machined crowned welding face with a ridge-containing surface.

FIG. 5 is an enlarged view of an electrode with a truncatedhemispherical tip portion and a crowned welding face with a machinedridge-containing surface.

FIG. 6 is an enlarged view of a portion of the face of the weldingelectrode of FIG. 3 showing two of the ridge rings and an intervening“flat” area in the welding face of the electrode.

DESCRIPTION OF PREFERRED EMBODIMENTS

A welding electrode cap (or welding face) design is provided that isuseful for forming spot welds in metal workpieces. The welding electrodecap is useful in spot welding operations generally, and it offersadvantages for welding light metal workpieces such as aluminum alloy andmagnesium alloy sheet materials. These materials often have an oxidefilm on surfaces contacted by the aligned and opposing electrodes and itis preferred that the electrode faces be shaped to engage and pierce theoxide film during welding.

In the manufacture of car doors, deck lids, liftgates, and the like, forexample, it is often the practice to form these parts of complementaryinner and outer sheet metal panels. The panels are of complex curvaturefor overall design effect and to contain any necessary electrical wiringand/or hardware between them. The formed panels usually have flanges attheir peripheral edges for joining. An inner panel is placed against anouter panel and the assembled workpieces positioned for the formation ofa series of progressively formed electrical resistance spot welds in abonding pattern along their flanges. In one type of welding operation,the assembled panels might be moved and positioned between the weldingarms of a stationary pedestal welding machine. In another type ofwelding operation, the assembled panels might be held in a fixedposition and a robot progressively move a welding gun around theperiphery of the workpieces to sequentially form the welds.

FIG. 1 illustrates a welding operation in which a spot weld is to beformed at a welding site 14 (shown as a dashed line weld nugget to beformed) in two juxtaposed aluminum alloy panels 10, 12 (only theoverlapping edges of panels 10 and 12 are shown for simplification ofthe illustration). An upper welding gun arm 16 has an electrode holder18 that holds welding electrode 20 in shank 22. The welding electrode isoften water-cooled by means not illustrated. Welding gun arm 16 is partof a fixed welding apparatus or robot-carried welding apparatus, notshown. A lower welding arm 24 is also carried on the welding apparatus.Lower welding arm 24 has an electrode holder 26 that holds weldingelectrode 28 in shank 30.

Welding electrode 20 carried by the upper welding arm 16 is shown inspot weld forming engagement with the outer (upper in FIG. 1) surface ofpanel 10 and welding electrode 28 carried by lower welding arm 24 isshown engaging the outer (lower) surface of panel 12. In a spot weldingoperation electrical current of suitable current value and duration ispassed between the tips of opposing and aligned electrodes 20, 28through the overlying panels 10, 12 at weld site 14. The electrodes 20,28 are pressed together, suitably in a predetermined pressure schedule,to press the panels 10, 12 together at the weld site 14 and to obtain asuitable preprogrammed momentary current flow for resistance heating ofthe metal at the weld site 14. Metal in the current path is momentarilymelted. The welding current is stopped; the molten metal rapidly losesheat to the water-cooled electrodes and the surrounding panel materialand solidifies as a weld nugget joining panels 10, 12 at weld site 14.The opposing electrodes 20, 28 are then withdrawn.

This welding sequence is usually completed in a matter of a second orso. The panels or electrodes are moved to a nearby weld site and theprocess is repeated until a suitable predetermined number of spot weldsare formed to secure panels 10 and 12. Then another workpiece assemblyis brought into proximity of the welding apparatus and a new sequence ofwelds formed. As will be described, the faces of the electrodes play arole in forming of each weld and in the efficiency of the ongoingwelding process.

The welding faces of the electrodes gradually become eroded and/oraccumulate unwanted deposits. The welding apparatus is then usuallytemporarily withdrawn from “on-line” operation so that the faces of theelectrodes can be repaired or an electrode replaced.

In this example, electrode 28 is identical to electrode 20, but theelectrodes are not necessarily the same shape. Electrode 20 is furtherillustrated in FIGS. 2, 3, 4, and 6. Referring to FIG. 3, electrode 20has a round body 40 with a hollow receptacle 42 adapted to receive ashank 22 for insertion into holder 18 of a welding arm 16. And electrode20 has a tapered transition section 44 with a spherically crownedwelding face 46. A series of concentric circular ridges 48 are formed inand constitute the welding face surface 46 of welding electrode 20. Thepattern of circular ridges 48 (or in another embodiment, grooves) mayextend onto the tapered surface 44 of electrode 20, but this is notillustrated in FIG. 3.

FIG. 4 illustrates a portion of the body 40 and tapered end portion 44of electrode 20 in cross-section. Referring to FIG. 4, and by way ofexample, the diameter (dimension A in FIG. 4) of electrode body 40 isoften about 12.5 mm to 22.2 mm. The diameter of the electrode body isusually not critical but it must be strong enough to withstand the 700to 1500 pound (or so) weld force applied for welding a variety ofaluminum gauges, and it must be at least the diameter of the weldingface 46.

The planar diameter (dimension B in FIG. 4) of the spherically crownedor domed welding face 46 of electrode 20 is, for example, between about6 and 12 mm. Welding face 46 may preferably be rounded or crowned withan exemplary radius (dimension C in FIG. 4) of about 25.4 mm.

A plurality of round concentric ridges 48 (FIGS. 3, 4, and 6) are formedin the spherically crowned welding face 46 of electrode 20. Theseringed-ridges 48 extend radially outward from the center of face 46, thelongitudinal axis (axis 47 in FIG. 6) of round cylindrical electrode 20.In a preferred embodiment, each contoured ridge 48 is nearlysemi-circular in cross-section (see FIG. 6), with its cross-sectionalcircumference arising upwardly from the surface of the crowned profileof face 46 with a sloped “flat” ring 49 (or base) on the sphericallycrowned surface between each contoured ridge ring 48. Of course, eachcontoured ridge 48 and each intervening flat ring 49 is of increasingradius as it is formed radially outwardly from the center of theelectrode face 46. By way of example, the diameter of the base of eachcontoured ringed ridge may be about 125 micrometers and the width ofeach intervening flat ring may also be about 125 micrometers.

In a preferred embodiment, the contoured rings are machined in thecrowned face of the electrode. As illustrated in FIG. 2, a single piececutter blade 50 is prepared with two cutting surfaces 52, 54 for cuttingupraised concentric rings in the welding face surfaces of two electrodes20, 28. The welding arms have positioned the welding faces of weldingelectrodes 20, 28 against the cutting surfaces 52, 54, respectively.This operation could be for the purpose of forming the concentric ringson new welding electrodes or for re-dressing the welding faces of usedelectrodes. The end 56 of the cutting surfaces 52, 54 of cutter blade 50extends to the aligned longitudinal axes of electrodes 20, 28.

Cutter blade 50 is carried in a rotating cutting tool (not shown) thatrotates the cutter blade 50 around the aligned center axes of theopposing electrodes. FIG. 3 presents an enlarged view of a portion ofFIG. 2 with the lower electrode 28 removed to better illustrate thelower cutting surface 54 of cutting blade 50. The end 56 of the blade isat the center axis of the aligned electrodes. The electrodes are pressedagainst the cutting surfaces 52, 54 of cutting blade 50 which rotatesaround its end 56 to cut concentric circular ridges 48 and interveningflat rings 49 and in the faces of the electrodes 20, 28.

Cutting surfaces of blade 50 are curved in complementary conformancewith the domed face surfaces of electrodes 20, 28 and provided withcutting surfaces for forming or re-forming the concentric contours inthe electrode faces. The cutter surfaces 52, 54 may be shaped byelectrical discharge machining or other suitable process to have curvedcircular cutter teeth 59 spaced by intervening “flat” (actually sloped)recessed cutter surfaces 58. Cutter teeth 59 and recessed cuttersurfaces 58 are sized and located along cutter surfaces 52, 54 forforming the contoured faces (e.g., face 46) in electrodes 20, 28. Cutterteeth 59 are illustrated in FIG. 3 as extending straight across cuttersurface 54 of cutter 50, but they may be curved for more accuratecutting of ridges 48 in electrode 20. The welding face of each electrodethen has formed upstanding concentric rings of ridges of semicircularcross-section separated by concentric flat ring spaces. Two of theseridges 48 with an intervening flat ring 49, starting from the center ofthe crowned face of electrode 20, are illustrated in FIG. 6.

The rings of ridges 48 start at the center of the round welding face 46and become progressively radially larger across the face. Ridges 48 areused to improve engagement of welding face 46 with the surface of a workpiece to be welded. They assist in gripping the workpiece andpenetrating a surface oxide layer. They improve electrical conductivityand reduce overheating and oxidation of the workpiece surface.

Electrode face ridges 48 may be formed in different continuousconcentric or spaced concentric shapes such as, for example, saw tooth(triangular) or sinusoidal shapes. While the formation of the contouredsurface has been illustrated by the use of a rotating cutter blade othersurface shaping methods may be used.

FIG. 5 illustrates (in cross-section) a different electrode shape with adifferent face contour. Electrode 60 has a round cylindrical body 62with a hemispherical tip 64 having the radius of the body portion 62.The hemispherical tip 64 is truncated and spherically crowned using alarger radius than the tip radius to form domed face 66 on the roundedhemispherical peripheral tip 64. By way of example, the diameter(dimension A in FIG. 5) of electrode body 60 may be about 12.5 to 22.2mm. The planar diameter (i.e., in plan view, dimension B in FIG. 5) ofthe welding face 66 of electrode 60 is, for example, about 6 to 12 mm.Welding face 66 may preferably be rounded or crowned with an exemplaryradius (dimension C in FIG. 4) of about 20 to 150 mm or greater. Theconcentric rings of ridges 68 formed in the welding face 66 are oftriangular cross-sectional shape. In this example no relatively flatring surfaces (like surfaces 49 in FIG. 6 on hemispherical face 46 ofelectrode 20) have been formed between the concentric, circular,radially spaced, triangular-cross section ridges 68.

The forming or dressing of the concentric rings of ridges or grooves onthe welding faces (and, optionally, the tapered side surfaces of thefaces) of the welding electrodes can be done following differentstrategies. Obviously, provision must be made in the original length ofthe electrode body and tip portions to accommodate repeated removal ofmaterial if the welding face of the electrode is to be repeatedlyredressed. For example, in one strategy, if the grooves/ridges on theelectrode can be brought into registry with the ridges/grooves on thecutting blade during dressing, then a small amount of metal can beremoved to refinish the electrode without completely re-cutting theridges/grooves. Experience in spot welding aluminum in production runshas shown that as little as 50 μm of metal can be removed to refinishthe weld face. Where the size of the electrode permits a total depth ofcut of 8 mm into the electrode face, which is also possible, this wouldresult in up to 160 dresses. Where obtaining registry between theelectrode and dressing blade is not possible and new ridges/grooves needto be cut for each dressing, then the size of the ridge/groove featuresshould be such that they can be cut without removing an excessive amountof the electrode face. In this case, to achieve a reasonable number ofdresses on an electrode (>40), less than ˜200 μm of metal would beremoved per dress and still maintain an adequate amount of copper (˜2mm) before penetrating the water passage. This would suggest that theridges/groove features to be machined into the electrode should have apeak-to-peak height of at most 200 μm. In general, to be effective theweld face should incorporate a minimal number of ridges/grooves, i.e.,three or more. To accommodate three concentric ridges/grooves on anelectrode face, for example, 8 mm in diameter the maximum spacingbetween each feature would be about 1500 μm. For complete re-cutting ofthe electrode face, the grooves/ridge features would most likely have apeak-to-peak height of 20 μm to 200 μm with a spacing of 80 μm to 1500μm, respectively.

Besides machining of grooves or ridges into the cutter face, the cuttercould be designed from the outset with a textured face such as a sawtooth wave or sine wave. This would be able to produce even roughersurfaces for a given peak-to-peak height of the texture, but may be muchmore difficult to produce than the previous designs.

A simpler alternative to machining grooves or ridges into the cuttingface of the blade would be to grind the cutting face with a roughgrinding tool that puts a random set of grooves and ridges into thedressing blade. During dressing, a mirror image pattern of thesefeatures will be produced on the electrode surfaces. Since registry ofthe features of the blade and electrode might be more difficult toobtain in this case, the peak-to-peak height of the machined bladeshould be less than ˜200 μm.

For blades that contain multiple cutting flutes (2 or more on a singleelectrode face), it may become apparent that the texturing pattern onthe cutting flutes does not produce the desired pattern on the electrodeface because it is not possible to perfectly align the flutes with eachother and the electrode face. In this case, only one of the cuttingflutes could be designed to produce the texture while the other flutesare machined so they do not contact the electrode face. Alternatively,the multiple flutes could be designed to each texture a different radialarea of the electrode face leaving the remainder of the faceundisturbed.

Use of welding electrodes with concentric contoured welding faces cansignificantly improve process robustness and weld quality for resistancespot welding of light metals. This is achieved by producinggeometrically consistent, clean electrode surfaces that will beperfectly aligned on the weld gun. In addition, the surface textureproduced on the welding electrodes will mechanically stabilize thewelding process and significantly reduce surface expulsion, which notonly harms weld quality, but detrimentally impacts paint surfacequality.

In general it is preferred to form welding electrodes of copper orcopper alloys because of the strength and electrical conductivityproperties which are very useful in making spot welds using electricalresistance heating.

The welding electrodes have been described in terms of certain preferredembodiments but other welding face shapes may be used.

1. A welding electrode comprising a body with a round weld face forcontact with a workpiece in an electrical resistance welding operation,the weld face comprising concentric rings of ridges or grooves formed inthe weld face, the concentric rings extending radially from the centerof the weld face.
 2. A welding electrode as recited in claim 1 in whichthe weld face comprises concentric rings formed in the weld face with acutting tool.
 3. A welding electrode as recited in claim 1 in which theconcentric rings are ridges with ridge height dimensions in the range oftwenty micrometers to two hundred micrometers and a spacing betweenridge heights in the range of eighty micrometers to fifteen hundredmicrometers.
 4. A welding electrode as recited in claim 1 in which theconcentric rings are grooves with groove depth dimensions in the rangeof twenty micrometers to two hundred micrometers and a spacing betweengroove depths in the range of eighty micrometers to fifteen hundredmicrometers.
 5. A welding electrode as recited in claim 1 in which theconcentric rings have a semicircular cross-sectional profile.
 6. Awelding electrode as recited in claim 1 in which the concentric ringshave a triangular cross-sectional profile.
 7. A welding electrode asrecited in claim 1 in which the concentric rings have a sinusoidalcross-sectional profile.
 8. A welding electrode comprising anelectrically conductive round body with an integral domed weld face forcontact with a surface of a light metal alloy workpiece in an electricalresistance welding operation, the weld face comprising concentric ringsof ridges or grooves integrally formed in the domed weld face forimpression into the workpiece surface, and the concentric ringsextending radially from the center of the weld face.
 9. A weldingelectrode as recited in claim 8 in which the body and integral domedweld face are made of copper or a copper alloy.
 10. A welding electrodeas recited in claim 8 in which the concentric rings are ridges withridge height dimensions in the range of twenty micrometers to twohundred micrometers and spacings between ridge heights in the range ofeighty micrometers to fifteen hundred micrometers.
 11. A weldingelectrode as recited in claim 8 in which the concentric rings are ridgeswith intervening flat bases on the domed weld face, the concentricridges having ridge height dimensions in the range of twenty micrometersto two hundred micrometers and spacings between ridge heights in therange of eighty micrometers to fifteen hundred micrometers.
 12. Awelding electrode as recited in claim 8 in which the concentric ringsare grooves with groove depth dimensions in the range of twentymicrometers to two hundred micrometers and spacings between groovedepths in the range of eighty micrometers to fifteen hundredmicrometers.
 13. A welding electrode as recited in claim 8 in which theconcentric rings are grooved valleys with intervening flat bases on thedomed weld face, the valleys having a valley depth dimensions in therange of twenty micrometers to two hundred micrometers and spacingsbetween valley depths in the range of eighty micrometers to fifteenhundred micrometers.
 14. A welding electrode as recited in claim 8 inwhich the concentric rings have a semicircular cross-sectional profile.15. A welding electrode as recited in claim 8 in which the concentricrings have a triangular cross-sectional profile.
 16. A welding electrodeas recited in claim 8 in which the concentric rings have a sinusoidalcross-sectional profile.
 17. A method of using an electrode inelectrical resistance welding, the electrode comprising a body with around weld face for contact with a workpiece in an electrical resistancewelding operation, the weld face comprising concentric rings of ridgesor grooves formed in the weld face for electrical contact with aworkpiece and extending radially from the center of the weld face; themethod comprising: contacting the electrode with one or more workpiecesto form a series of electrical resistance welds; determining whenconcentric rings in the weld face have been degraded for suitableelectrical contact with a workpiece; reforming the concentric rings;and, thereafter continuing to form welds with the electrode.
 18. Amethod as recited in claim 17 in which the electrode has a round domedweld face.
 19. A method as recited in claim 17 in which a cutting toolis used to re-form
 20. A method as recited in claim 17 in which acutting tool is rotated in engagement with the electrode face to re-formthe concentric rings.
 21. A cutting tool for forming concentric rings ofridges or grooves in a round weld face portion of an electricalresistance welding electrode, the cutting tool comprising: a cutterblade having a portion for carrying the cutter blade for relativerotation with respect to the weld face portion of a welding electrodeand at least one cutting surface for forming the concentric rings ofridges or grooves in at least one welding electrode, each cuttingsurface being shaped for engagement of the round face portion of thewelding electrode from its center to at least the radial extent of theconcentric rings of ridges or grooves and having cutting surfacefeatures corresponding to a predetermined shape of the round weld faceportion of the electrode, the cutting surfaces being shaped to cut apredetermined pattern of the concentric rings of ridges or grooves uponsuch relative rotation.
 22. A cutting tool as recited in claim 21 inwhich the cutting surface features are shaped to form ridges with ridgeheight dimensions in the range of twenty micrometers to two hundredmicrometers and spacings between ridge heights in the range of eightymicrometers to fifteen hundred micrometers.
 23. A cutting tool asrecited in claim 21 in which the round weld face portion of theelectrode is domed and the cutting surface features are shaped to formridges with intervening flat bases on the domed weld face, theconcentric ridges having ridge height dimensions in the range of twentymicrometers to two hundred micrometers and spacings between ridgeheights in the range of eighty micrometers to fifteen hundredmicrometers.
 24. A cutting tool as recited in claim 1 in which thecutting surface features are shaped to form grooves with groove depthdimensions in the range of twenty micrometers to two hundred micrometersand spacings between groove depths in the range of eighty micrometers tofifteen hundred micrometers.
 25. A cutting tool as recited in claim 21in which the round weld face portion of the electrode is domed and thecutting surface features are shaped to form grooved valleys withintervening flat bases on the domed weld face, the valleys having avalley depth dimensions in the range of twenty micrometers to twohundred micrometers and spacings between valley depths in the range ofeighty micrometers to fifteen hundred micrometers.